This invention relates generally to the controlled cooling of the molten flat glass ribbon as it passes through the tin float bath at a continuous rate. Manufacturing flat glass comprises the delivering of molten glass to a bath of molten tin and advancing the glass along the surface of the tin under thermal conditions that do not contaminate the internal atmosphere. Such contamination is detrimental to both the glass product and the molten tin. Glass at approximately 1900 degrees F enters the bath from the melting tank and at approximately 1200 degrees F exits the bath to a cooling lehr. In prior art installations the temperatures in the bath are maintained with electrical resistance heaters suspended from the roof over the ribbon of glass. Such electrical heaters do not contaminate the bath atmosphere. The metal plate shell of the prior art bath roof is protected from the heat with an internal refractory lining, which has little or no heat-insulating qualities and isolates the electrical equipment plenum above from the heated cavity. This prior art construction has been used over the past twenty-five year period. Attempts to burn natural gas over the bath by the glass industry failed the industry's contamination requirements.